"Bio-based" is one of the most common words on sustainable packaging — and one of the most misunderstood. It describes where a material's carbon comes from, not what happens to it after use. A product can be fully bio-based and never break down, or partly fossil-derived and still compost.
The number behind the claim is measured by ASTM D6866, using radiocarbon analysis. Carbon in living plants contains the isotope carbon-14; carbon from fossil fuels contains essentially none, because it decayed away over millions of years underground. A laboratory measures the ratio of carbon-14 to carbon-12 in a sample and reports biobased carbon content as a percentage of total organic carbon. The equivalent international standard is ISO 16620-2.
The U.S. Department of Agriculture's BioPreferred program uses D6866 testing to set minimum biobased content for product categories: 25% for product packaging, 72% for disposable containers, and 48% for disposable cutlery. Products must pass independent third-party testing before they can carry the USDA Certified Biobased Product label.
That percentage says nothing about end of life. Bio-based polyethylene, made from sugarcane ethanol, is chemically identical to conventional polyethylene: it recycles in the same stream and persists just as long. PBAT, the flexible polymer often blended with PLA in compostable films, is usually made from oil-derived monomers — yet it is certified industrially compostable. PLA sits in the overlap: plant-derived and industrially compostable.
So when a supplier quotes a bio-based percentage, ask for the second number too: compostability certification to ASTM D6400, EN 13432, or GB/T 19277, under industrial composting conditions. At Greenstar, our compostable bags carry those certifications. The bio-based figure and the compostability certificate answer two different questions — and a buyer needs both.
Disclaimer: Product descriptions, specifications, and certification references in this article are provided for general information. Compostability claims (including ASTM D6400, EN 13432, and GB/T 19277) refer to industrial composting conditions; commercial composting facilities may not be available in all communities. Certifications apply only to the specific products listed in the relevant certificates. For current certification documentation, contact Greenstar@greenstarmaterial.com.